We plan to study the gene structures of several tRNAs which are found in virions of RNA tumor viruses. The tRNA genes have been isolated from an R1 library of mouse cell DNA. The genes will be analyzed for intervening sequences, expression (both in vivo and in vitro) and for possible association with other tRNA genes. A similar study will also be carried out on genes encoding small nuclear RNAs of mouse cells. We plan to use these cloned genes for assaying possible changes in the metabolism of these RNAs during infection or transformation of cells by RNA tumor viruses.